DESCRIPTION (Adapted from the Abstract): The ovarian steroid hormones, estradiol and progesterone, regulate physiology and behavior, including estrous behavior, in a variety of species. Much evidence supports the idea that one mechanism by which these hormones act in the brain is by way of binding to, and subsequent activation of, hormone-specific receptors which may then act as cell nuclear regulators of gene expression. Although steroid hormone receptors are known to be regulated by steroid hormones, evidence suggests that afferent input into steroid hormone-sensitive neurons can influence neuronal and behavioral response to steroid hormones. Under some circumstances, afferent input may regulate the concentration of receptors and, in other cases, it may activate receptors, resulting in neuronal changes that are dependent upon receptors. In the proposed experiments, two interactions between afferent input and steroid hormone receptors will be explored. First, the role of progestin receptors in mediating neuronal response to afferent input will be examined and, then, the regulation of progestin receptors and subsequent estrous behavior by afferent input coming from mating stimulation will be studied. In the first set of experiments, mating stimulation will be used as an external, physiologically-relevant stimulus with effects on steroid hormone-sensitive neurons. The hypothesis to be tested is that some of the neuronal responses to mating stimulation are mediated by activation of intracellular progestin receptors. In the second set of experiments, the hypothesis to be tested is that afferent stimulation of progestin receptor-containing neurons influences subsequent estrous behavior and expression of both protein products of immediate early genes and progestin receptors. In the third set of experiments, the hypothesis to be tested is that catecholaminergic neurotransmitters mediate the effects of mating stimulation on estrous behavior and on neuronal responses of progesterone-sensitive neurons. The Investigator hypothesizes that progestin receptor-containing neurons exist that are responsive to mating stimulation and that also contain subtypes of catecholaminergic receptors. In these neurons, afferent input by way of catecholaminergic receptors may influence progestin receptor function, and consequently behavior and physiology.